It's considered a good style to test only one thing per test in ruby. Also the test output isn't very readable atm, as it doesn't explain what the controller is expected to do. Suggestion:

```ruby
describe SingleWidgetController do
  describe '#create' do
    it 'creates a new shortened URL' do
      expect { ... }.to change{ ... }.by(1)
    end

    it 'returns a JSON object with the generated widget slug' do
      ....
    end
  end
end
```